The use of liquid crystal displays has been rapidly increasing in a variety of fields as low-power, thin and light-weight displays. In particular, in the mobile phone field which has seen an explosive growth in recent years, every mobile unit is equipped with a liquid crystal display.
In mobile phones, reflective liquid crystal displays are often employed because of their low power consumption in order to extend battery life. Most of them are transflective liquid crystal displays equipped with backlighting. Since liquid crystal displays are not self-luminous displays, the backlight is used to enhance visibility in a low-light environment where a sufficient amount of ambient light is not available for viewing the screen.
In recent years, as information communications such as electronic mail develop, the screen size of the liquid crystal display has been increasing and, as a result, the size of the mobile phone also has been increasing. In view of this, folding mobile phones have been developed that offer the advantage of being able to protect the display screen as well as the advantage of enhancing the portability.
Since this type of mobile phone is usually folded up when not in use, the user has had to unfold the phone each time he or she wants to check the current time or to check for an incoming call. To eliminate such inconvenience, recent mobile phones have come to be equipped with, in addition to a first liquid crystal display which is viewed with the mobile phone unfolded, a second liquid crystal display which is mounted in a position where the display can be viewed with the mobile phone folded up, thus enabling the user to check various kinds of information displayed thereon anytime he or she desires.
FIG. 16 is a diagram showing an example of the construction of a commonly used mobile phone.
The mobile phone 1000 comprises a main body 1100 and a cover 1200 joined together by a hinge 1300 in such a manner that the cover can be turned to open and close relative to the main body. A keypad 1109 is provided on the top of the main body 1100, and a first liquid crystal display 1101 and a second liquid crystal display 1102 are mounted in the cover 1200 in a back-to-back arrangement thus forming a double-sided display apparatus.
The first liquid crystal display 1101 comprises a first display panel 1103 and a first backlight 1104, and the second liquid crystal display 1102 comprises a second display panel 1105 and a second backlight 1106. A first windshield 1107 and a second windshield 1108 are provided on the casing of the cover 1200, the former on the inside (the right side in the figure) and the latter on the outside (the left side in the figure), in order to allow the respective display panels 1103 and 1105 to be viewed therethrough.
The display functions of the mobile phone 1000 shown in FIG. 16 will be described. When the user uses the mobile phone 1000, the user opens the cover 1200 folded over the main body 1100 by turning the cover 1200 in the direction indicated by arrow. In this case, the first display panel 1103 produces the display, and the first backlight 1104 is turned on. At this time, the second display panel 1105 also produces a display, but the second backlight 1106 is off. In this condition, the user can operate the keypad 1109 on the main body 1100 while viewing the display produced on the first liquid crystal display 1101.
When folding up the mobile phone 1000 for portability, the user turns the cover 1200 in the direction opposite to the direction of the arrow and thus folds it over the main body 1100. Thereupon, the display on the first display panel 1103 turns off, and the first backlight 1104 also turns off. On the other hand, the display on the second display panel 1105 remains on, and the second backlight 1106 now turns on. The second backlight 1106, however, turns off several tens of seconds after that. The second backlight 1106 also turns on when an incoming call arrives or when the user operates a key or the like.
FIG. 17 is a diagram schematically showing another prior art liquid crystal display apparatus (see patent document 1).
In the liquid crystal display apparatus shown in FIG. 17, a light source 58 as a backlight 51 and a light-guide member 49 are provided between a first display panel 40 and a second display panel 50.
The first display panel 40 is a monochrome transflective liquid crystal display. A liquid crystal layer 44 is sealed between a transparent front substrate 41 and a transparent rear substrate 42 by means of a seal member 43. A transflective film 45 is provided on the surface of the transparent rear substrate 42 that faces the liquid crystal layer 44, and a polarizer 46 is provided on the front surface of the transparent front substrate 41.
The second display panel 50 is a transmissive color liquid crystal display. A liquid crystal layer 55 is sealed between a transparent front substrate 52 and a transparent rear substrate 53 by means of a seal member 54. Color filters 56 are provided on the surface of the transparent rear substrate 53 that faces the liquid crystal layer 55, and polarizers 57 and 58 are provided on the front surface of the transparent front substrate 52 and the back surface of the transparent rear substrate 53, respectively.
In FIG. 17, electrodes and alignment films or insulating films (or planarizing films) are provided on the liquid crystal sides of the respective substrates.
In FIG. 17, external light S incident on the first display panel 40 passes through the polarizer 46, the liquid crystal layer 44, etc. and is reflected by the transflective film 45; the reflected light passes through the liquid crystal layer 44 and through the polarizer 46 for viewing by the viewer. In this way, the first display panel 40 functions as a reflective liquid crystal display.
On the other hand, when the backlight 51 is turned on, the light from the backlight, when directed toward the first display panel, passes through the light-guide member 49, the transflective film 45, and the liquid crystal layer 44, and is thus viewed as light S′ by the viewer.
The second display panel 50 is a transmissive color liquid crystal display. When the backlight 51 is turned on, the light S1 directed in the direction of the second display panel 50 travels in that direction to provide a light source for the second display panel 50. The light directed in the direction of the first display panel 40 passes through the transparent substrate 42 of the first display panel 40, but a portion of the light here is reflected by the transflective film of the first display panel 40 back into the direction of the second display panel 50 to provide a light source for the second display panel 50. On the other hand, the remaining light that passed through the transflective film is blocked by the liquid crystal layer 44 and does not reach the viewer. In this way, half of the light emitted from the backlight 51 is used as the light source for the second display panel 50.
FIG. 18 is a diagram schematically showing still another prior art liquid crystal display apparatus (see patent document 2).
The liquid crystal display apparatus shown in FIG. 18 comprises a liquid crystal panel 64 which is constructed by sealing the outer peripheral edges of a first transparent substrate 60 and second transparent substrate 61 by a seal member 62, with a liquid crystal material, as a liquid crystal layer 63, sandwiched therebetween.
An integrated circuit 65 for driving the liquid crystal display is connected, via an anisotropic conductive layer 67 containing conductive particles 66, to the underside of the first transparent substrate 60 at a position outwardly to the right of the seal member 62 as seen in the figure. A light control layer 68 is formed on the viewer side (the upper side in the figure) of the first transparent substrate 60. The light control layer 68 is formed over the entire area on the surface of the first transparent substrate 60 except the portion thereof to which the integrated circuit 65 is connected.
A first polarizing member 71 comprising a first polarizer 69 and a retardation film 70 is disposed above the light control layer 68. An internal reflective layer 72 is formed on the surface of the second transparent substrate 61 that faces the liquid crystal layer 63. A light source 73 is disposed in such a manner as to closely contact the left end face of the first transparent substrate 60 via a second polarizer 74 and a second retardation film 75.
In the structure of FIG. 18, the first transparent substrate 60 is formed thicker than the second transparent substrate 61. The first transparent substrate 60, on the upper surface of which the light control layer 68 having projections and depressions is formed, is attached to the first polarizing member 74 by means of a attaching member 76 on the light control layer 68.
Patent document 1: Japanese Unexamined Patent Publication No. 2004-45727
Patent document 2: Japanese Unexamined Patent Publication No. 2001-75087